Ground zero

20:44, Jan 24 2013
Strong back needed: The aim is to cultivate friable loam.

A reader took me to task for last week's column, objecting to my careless use of dirt as a synonym for soil.

I would argue that "dirt" is merely the vernacular and in no way demeans the gravitas of soil, but it did get me thinking about the natural growing medium beneath our feet.

I also found a wonderful throwaway comment in the same book that gave this week's gardening quote - The Curious Gardener's Almanac.

Following from the adage of "look after the soil and the soil will look after the plants" was a variation on the theme: "Feed the soil, not the plants".

Yes, I thought. That was a message that spoke to me. We swim against the modern tide and rarely use garden fertiliser here, preferring instead to rely on homemade compost.

Garden soil must be the least sexy and interesting part of gardening for the novice. Yet every experienced gardener, without exception, will tell you that the state of your garden soil is critical to the end result with the plants. It is just that the plants are a lot more interesting, so beginner gardeners start with them.


There can be a lot of fatalities before they work out that the state of the soil may need some serious attention.

The current craze for no-dig gardening is another issue altogether to which I may return in the future, but whether you opt to plant in the ground or on top of the ground, the growing medium that houses the roots of all your plants is critical.

We are in-ground gardeners here and are lucky to be on free-draining, fine, volcanic loam, which is one of the easiest natural mediums of all with which to work. Others are nowhere near as lucky.

At the ends of the spectrum are the fine, sandy soils (predominantly in coastal areas) and heavy clay.

The former lacks in humus and does not retain moisture or nutrition. The latter holds too much moisture in wet times, but can take on a concrete-like consistency in dry times. Clay lacks aeration, making it difficult for plant roots to function well.

New housing subdivisions often end up with deeply inhospitable soils. In the past, developers were renowned for removing the top soil and then selling it back later when the homeowner wanted to start a garden. I have no idea if that is true, but where excavation has been necessary, developers are unlikely to understand the need to set the top soil layer aside to put it back it in its rightful place on top when the site is levelled again.

They are more likely to mix it all up, so you end up with the sub stratas (often heavy clay) dominating the top layers.

If you are new to gardening and are not at all sure what your soil is like, take a walk around your neighbourhood. If you have neighbours, you are sure to find one out in their garden and most will be glad to give you advice. Soil types vary widely, but if you are in dairying territory, you are likely to have better soils.

If your soils are less than ideal, set aside the prepackaged or processed fertilisers. They are a short-term fix for short-term plants, but won't do anything at all for your soil structure.

Sandy soils which dry out very quickly lack humus and sustenance for plants. There are probably very few worms, yet these wrigglers play an important role in mixing up and aerating the soil. You can alter the structure, but it takes work and time. You need to load in the compost, leaf litter, grass clippings, seaweed and any other natural material which will add substance to the soil. Keep at it over time too. It is not a one-off task.

Animal manures should be left to age before you bury them in the soil. They are too strong when they are fresh and can burn plants. You can dig a trench and bury your kitchen scraps directly into the ground. You are just trying to get as much organic material into the soil. Then the worms will arrive, along with all the other natural microbial action and insect life of healthy soils.

Clay soils also suffer from a lack of worms, but, as a rule, they are not lacking in nutrients. Basically, the aim is to break up the clay to allow for better drainage, increased worm activity and aeration.

Adding gypsum is one strategy. Bringing in very fine gravel or sharp river sand is reputed to help, but you are likely to need several centimetres of it to make any difference and it will need to be dug through the clay. Otherwise, do the same as for sandy soils and bring in mountains of humus. Build up your layers on top. The worms will arrive and start to do some of the work for you.

You are trying to speed up a natural process where top soil builds up closest to the surface, giving you friable and fertile conditions in which to grow plants.

None of this is rocket science.

It just takes time, effort and a strong back if you are starting with impoverished soil.

In gardening, you often have to take the longer-term view.